Ketonization of enols in aqueous solution: is carbon protonation always rate-determining?
| Authors | |
|---|---|
| Year of publication | 2012 |
| Type | Article in Periodical |
| Magazine / Source | PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES |
| MU Faculty or unit | |
| Citation | |
| Web | Full Text |
| Doi | http://dx.doi.org/10.1039/c2pp05369a |
| Keywords | KETO-ENOL; DISSOCIATION-CONSTANT; BUFFER SOLUTIONS; ACID; HYDRATION; SYSTEM |
| Description | The pH-rate profiles for the ketonization of the (E)- and (Z)-photoenols of o-methylacetophenone (MA) in aqueous solution were determined by nanosecond laser flash photolysis. Carbon protonation of the enol anions of MA by solvent water is exceptionally fast, k(0)'K approximate to 2.0 x 10(7) s(-1), too fast to permit establishment of the acid-base equilibrium on the enol oxygen prior to ketonization. Analysis of the pH-rate profile of the (E)-enol using the common assumption of rate-determining carbon protonation would lead to an erroneous value for the acidity constant of that enol, pK(a,c)(E) = 11.3, which is too high by about two pK units. |
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